1. Technical Field of the Invention
The field relates generally to a two-dimensional (2D) Hall sensor array with high spatial, magnetic field and time resolution, for detecting spatially varying and time-dependent magnetic fields and, more particularly, to a system and method for individually addressing Hall sensors from a plurality of integrated Hall sensors and perceiving their individual response to a magnetic environment for magnetic field mapping, more particularly for high-precision positioning and magnetic field detection and imaging of magnetic field variations in time or in space.
2. Description of the Related Technology
Existing magnetic field detecting devices based on SQUID, GMR and Hall effect sensors are currently available only as individual sensors or one-dimensional arrays. This inevitably involves the need of either two-dimensional or one-dimensional scans if the spatial variation of the local magnetic field over a two-dimensional area has to be mapped. Such scans are sequential by definition and therefore are slow and time-consuming processes.
The most widely used magnetic field sensor is the Hall effect sensor. This sensor provides a very fast response and high sensitivity. It is quantitative, non-invasive and applicable in a large temperature range and in external magnetic fields.
Nowadays, Hall sensors are commonly used in a broad range of applications such as remote switches, flow rate sensors, sequencing sensors, proximity sensors, position sensors, speed sensors, brushless DC motor sensors, RPM sensors, current sensors, temperature or pressure sensors, magnetic card readers, throttle angle sensors in cars, automotive sensors, etc.
In most of these applications, one or more permanent magnets are used in combination with one or more individual Hall sensors and their relative displacement is being measured through the output of the Hall sensor or sensors.
Another application is Scanning Hall Probe Microscopy (SHPM) in which an individual Hall sensor is scanned over a magnetic surface in order to construct a two-dimensional image of the magnetic field distribution.
However, most existing Hall-sensor-based devices make use of either individual sensors or their one-dimensional arrays. Positioning of a magnetic object, for example, such as a permanent magnet, is currently being performed with a limited number (one or two) of individual Hall sensors, resulting in a limited position resolution.
A two-dimensional array of Hall-effect based magnetic field sensors is described in EP-1 469 311 A1. The Hall effect sensors in this array are formed by the channel of a Metal-Oxide-Semiconductor (MOS) structure, which allows them to be switched on and off. However, MOS Hall effect devices have some serious drawbacks: the carrier mobility in the channel is only half its value in the bulk of the semiconductor; the 1/f noise of a MOS device is usually several orders of magnitude higher than that of a comparable bulk device; and the surface might be insufficiently stable [R. S. Popovic, Hall effect devices, magnetic field sensors and characterization of semiconductors, Adam Hilger, 1991].
A two-dimensional array of magnetic field gradient sensitive sensors is also described in DE-199 48 618 B4. The sensor elements in this array use the Hall effect in order to detect a magnetic field gradient along a specific direction. These sensors are only sensitive to the gradient and not to the magnetic field itself.